1. You have prepared lipid vesicles that contain molecules of the K+ leak channe
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Question
1. You have prepared lipid vesicles that contain molecules of the K+ leak channel, all oriented so that their cytosolic surface faces the outside the vesicle. Predict how K+ ions will move under the following conditions and what sort of membrane potential will develop?
a. Equal concentrations of K+ are present inside and outside the vesicle.
b. K+ ions are present only inside the vesicle.
c. K+ ions are present only outside the vesicle
2. A model for uniporter that could mediate passive transport of glucose down its concentration gradient is shown below. How would you need to change the diagram to convert the transporter into a pump that transports glucose up its concentration gradient by hydrolyzing ATP?
I need help with the illustration pls????
Explanation / Answer
Hi,
Out of the cell. K+ is the principle cation inside a cell, so it will flow out through a channel . Promote. The concentration of K+ is a lot higher inside the cell, and is low outside, thus creating a gradient. K+ will try to diffuse out of the cell to reach equilibrium. The gradient promotes this.Think about a battery, a neuron with its membrane potential is similar to a battery. K+ has more electrons, thus is more electronegative, while Na+ has fewer, thus is more positive. So the inside of the cell, with more K+, is electronegative. What does a battery want to do when the circuit is completed? Electrons from the negative end flows to the positive end. Thus, just like an electron, the K+ will want to flow through. Membrane potential promotes the movement. It decreases the membrane potential.
a)Cells need many amino acids, sugars and other substances that may be in low concentrations outside the cell membrane.Active transport is the movement of a substance against the concentration gradient of the substance.
Active transport requires cell energy! (ATP)
Some active transport processes use carrier proteins as pumps, and are sometimes called membrane pumps.
Pumps use energy - hydro and windmills, air pump, aquaculture pump.In animal cells, the sodium potassium pump is a carrier protein that uses energy supplied by ATP to transport sodium ions out of the cell and potassium ions into the cell.Na+ ions are usually more concentrated outside.K+ are more concentrated inside.
1. The pump transports three Na+ ions out for each molecule of ATP (the phosphate binds to the pump.
2. The phosphate molecule makes it change shape and the Na+ molecules are released outside.
3. Two K+ ions bind to the pump, and cause it to change shape.
4. The phosphate group is released, and the K+ ions are also released.
This prevents sodium from accumulating in the cell (they accumulate through ion channels), drawing water through osmosis and bursting the cell.This also helps maintain the sodium and potassium ion gradient, which often drive the transport of other molecules (including glucose) across the membrane.Hydrogen ion pumps are important to making ATP.
b)
Lipid vesicles (small spherical bilayers) provide an ideal in vitro system for the study of
pumps and channels. You have prepared lipid vesicles that contain Na+/K+ pumps. The pumps are
oriented such that the portion of the pump that normally faces the cytoplasm is facing the outside of the
vesicle. Predict what would happen under each of the following conditions (for simplicity, assume that
the ions are pumped in a 1:1 ratio).
A) The solution on the inside and outside of the vesicles contains both ions, but no ATP.
B) The solution inside the vesicle contains both ions; the solution outside contains both ions and
ATP.
C) The solution inside contains sodium ions; the solution outside contains sodium ions plus ATP.
D) The solution as in part B, but the pumps are randomly oriented, some facing outward and some
facing inward.
c)A neuron receives millions of synaptic inputs from other neurons. These inputs serve either to excite (open positively charged Na+ channels) or inhibit (opens negatively charged ion channels). (excitation or inhibition by the way is due to the specific receptor that is present and the ion channel that it is linked to - thus a dopamine D1 receptor could excite a neuron while a D2 receptor could inhibit the cell). Once there is enough excitation (i.e. there are enough channels open to allow sufficient postively charged sodium ions to enter the cell at the axon hillock, the
action potenial "travels" down the axon. At the end of the axon,voltage dependent calcium channels open which allow a flood of calcium in which directs the vesicles to the synapse where the membrane of the vesicle fuses
with the membrane of the axon and dumps its neurotransmitter in the synaptic cleft. --This is an all or none reaction, thus once the action potential begins to travel down the axon, it continues down the entire axon. It cannot stop half way, and its strength does not diminish.
Remember there are both Na+ and K+ ions and Cl- ions located both inside and outside of the cell membrane. In the resting state there are more negatively charged ions inside the cell (polarization). Depolarization or an action potential occurs when the charge (or voltage) inside the cell changes from a negative charge to a positive charge.
2) The plasma membrane is a selectively permeable barrier between thecell and the extracellular environment. Its permeability propertiesensure that essential molecules such as glucose, amino acids, andlipids readily enter the cell, metabolic intermediates remain in the cell, andwaste compounds leave the cell. In short, the selectivepermeability of the plasma membrane allows the cell tomaintain a constant internal environment. In severalearlier chapters, we examined the components andstructural organization of cell membranes. The phospholipid bilayer the basicstructural unit of biomembranes is essentiallyimpermeable to most water-soluble molecules, such asglucose and amino acids, and to ions. Transport of suchmolecules and ions across all cellular membranes ismediated by transport proteins associated with theunderlying bilayer. Because different cell types requiredifferent mixtures of low-molecular-weight compounds,the plasma membrane of each cell type contains a specificset of transport proteins that allow only certain ions ormolecules to cross. Similarly, organelles within the celloften have a different internal environment from thatof the surrounding cytosol, and organelle membranescontain specific transport proteins that maintain this difference.
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